The National Institutes of Health (NIH) has launched two of three Phase III clinical trials to assess the safety and effectiveness of different blood thinners to treat adults with Covid-19.

These trials are part of NIH’s Accelerating COVID-19 Therapeutic Interventions and Vaccines (ACTIV) initiative and will be carried out at more than 100 sites globally.

Participants to be enrolled are patients who have not been hospitalised, those currently hospitalised, and those discharged following hospitalisation for moderate to severe Covid-19.

The studies for hospitalised patients and for those who have not been hospitalised have launched, with the trial for those discharged after hospitalisation yet to start.

Known together as ACTIV-4 Antithrombotics, the trials are designed to gain insights that could help care for Covid-19 patients, especially those with potentially fatal blood clots.

Funded through the US Government’s Operation Warp Speed programme, the studies will be led by the National Heart, Lung, and Blood Institute (NHLBI).

According to research data, several patients who have died from Covid-19 developed blood clots throughout their bodies. This clotting was found to be responsible for organ damage, heart attack, stroke and pulmonary embolism.

Blood thinners, also called antithrombotics or anticoagulants, prevent blood protein and platelets from forming clumps.

However, further research is necessary to determine if and when during the course of Covid-19 blood thinners could help treat the disease.

The ACTIV-4 Antithrombotics Inpatient trial will evaluate the safety and effectiveness of different doses of the blood thinner heparin to prevent clotting events and improve outcomes in hospitalised patients.

Meanwhile, ACTIV-4-Antithrombotics Outpatient will assess if anticoagulants can mitigate fatal cardiovascular or pulmonary complications in newly diagnosed patients who do not need hospitalisation.

Participants will be given a placebo, aspirin, or a low or therapeutic dose of blood thinner apixaban.

The adaptive design of the trials will allow the addition, removal or combination of various blood thinners based on the study findings.

NHLBI Division of Blood Disorders and Resources director Keith Hoots said: “We must use therapies that support the natural inhibitors of clotting in the blood.

“Heparin has shown promise, but we really need clinical trial data to determine how much blood thinner, or even anti-platelet medication, to give.”

Last month, NIH started a Phase III trial, named ACTIV-3, to investigate various types of monoclonal antibodies as potential treatments for hospitalised Covid-19 patients.